In general, conductive panels of the foregoing type consist of a carrier or support comprised of an insulating material, e.g., a molded laminate material comprised of impregnated paper or glass fabric, which supports conductive pathways on its surface or embedded in the carrier, and, where necessary, in two or more planes. Likewise, conductive panels of this type are normally provided with perforations, the walls of which have a metallic layer in mechanical and electrical contact with associated conductive paths.
It has been proposed to make use of a metallic material as a base for the conductive paths, in which the metallic carrier is, first of all, provided with perforations, the walls of which are to carry a metal layer in the finished conductive panel. The surface, inclusive of the walls of the holes, is then provided by the whirl-sintering method with a layer of insulating material, to which the conductive paths are then applied.
Conductive panels having a carrier comprised of metal, the conductive pathways of which are made after the style of printed circuits in a known manner by subtractive or additive methods, or combinations of such methods, possess a number of disadvantages, however. For the application of the whirl-sintering layer elaborate apparatus and complicated techniques differing fundamentally from ordinary methods of production of conductive panels, are needed. Moreover, the application of the insulating layer by the whirl-sintering methods leads to an hour-glass-like shape in the walls of the holes.
In order to achieve useful thicknesses for the insulating layer at the edges of the holes it is necessary to tolerate relatively very thick insulating layers on the surface and in the middle of the hole. In addition, because of the peculiarity of the structure of the insulating layer, it is necessary to start off with holes of a relatively large diameter in the metal carrier. The poor utilization of the surface as a result is opposed to the construction of conductive panels having a high density of conductive paths. The employment of modern electronic component parts requires conductive panels having high conductive path density, however.
It has been proposed to perform the line-up by means of electrophoresis. Apart from this technique being unusual in conductive panel technology, and, moreover, relatively elaborate, the aforementioned disadvantages also occur. In particular, it is difficult or impossible to achieve a uniform coating in the walls of the holes.
The application of insulating layers by flame spraying and other methods proposed in the prior art has, likewise, not let to any technically and economically useful results.
For metal carriers comprised of aluminum, it has been proposed to apply an insulating layer by means of electrooxidation. But the resulting layers of insulating material possess mechanical properties which are not suitable for the production of conductive panels comprised of metal carriers.
For conductive panels in which the material of the conductive paths consists of a preformed wirelike material provided with an insulating layer, the wirelike material of the conductive paths is applied first, in order to apply drilled holes which pass through the appropriate conductive paths and which are carried into or, respectively, through the carrier material. Pre-perforated carrier panels provided with an insulating layer by whirl-sintering or in some other way with holes the walls of which are equipped with an insulating layer, are therefore, fundamentally unsuitable for the production of conductive panels of this type.
On the other hand, there exists a need for conductive panels of this kind because of the high strength thereby achievable, and also because the newer semiconductor components have made possible an extraordinary miniaturization of electronic apparatus the limits to which are determined, however, by the dissipation of heat.
Conductive panels having a base comprised of a molded material and the like are distinguished by relatively poor heat conductivity and, hence, heat dissipation, whereas the use of metal carriers leads to a fundamental improvement in this respect.
An object of this invention is to provide methods for producing electrically conductive panels having metal carriers which are free of the afore-stated disadvantages of the prior art and which are useful for the production of conductive panels the conductive pathways of which consist of a preformed wirelike material. This object is realized by this invention, which is described herein.